Many sites have existing voice-grade twisted pair copper cabling installed between buildings and out-houses. These cables are often overlooked as an IP CCTV system networking solution because they don't meet the requirement of modern fast Ethernet systems (Cat 5/6) and the total run may exceed the 100m distance limit permitted by the 802.3 specification.
Ethernet extenders use DSL technology (similar to that used to provide broadband internet access to your home - ADSL) to extend Ethernet connections over a single twisted-pair up to a maximum distance of 13km.
This solution can save a large sum in cable installation costs when adding remote controllers / cameras to access control systems or IP CCTV networks. It is possible to use an existing RS485 twisted pair previously employed for PTZ signalling to upgrade your existing camera connection to an IP compliant one.
The diagram above gives an example of an application for Ethernet extenders to extend a connection to two remote IP cameras in an IP video surveillance system. Extenders operate 'intelligently' at the physical layer passing frames across the twisted pair only when they are destined for a device at the far end. Single devices or entire LANs can be connected to each other. Additional connections are provided by adding an Ethernet switch at one or both ends.
DSL technology provides an optimum trade-off between distance and data rate. As with all signalling technologies, the greater the distance, the lower the achievable throughput. The table below provides typical distance vs. bandwidth characteristics for Ethernet extenders.
* This table provides a limited example of the options available. Asymmetric settings, favouring download speeds, are also available.